While scouring the far corners of the internet, we often run across tools that look great but come up just short of making the cut for a post. For example, I've been keeping my eyes on a few Firefox extensions lately that I love, but they're still in Experimental mode on Mozilla, meaning that you need to register with Mozilla and sign in to download them—because Mozilla testers haven't yet gotten around to approving them to go public just yet. We pass on these to make sure anything we post is readily available to our readers. Rather than continue to wait, which can take a while with Mozilla's approval process, check out three of my favorite experimental Firefox extensions.

Note: Mozilla hasn't officially approved these extensions, so do proceed with caution.

Picture in Picture

The Picture in Picture extension, aka PiP, overlays videos from sites like YouTube in the corner of any other tab. That way you can keep an eye on the video while you're going about the rest of your browsing business. You can set your preferred size for the picture-in-picture video to make it as small or large as you want, and PiP works with several different video sites, from YouTube and Google Video to Funny or Die. (It's still a touch buggy on others.) To enable PiP, just click the small TV icon on your statusbar while you're watching a video. This one could still use a little polish around the edges, but it's also unquestionably brilliant. The downside: Currently it's Mac only.

FlickrSendr

The FlickrSender extension sideloads any image in your browser directly to your Flickr account. That means that next time your sister sends you a few cute pictures of her baby via email, or you see an image that you'd really like to keep (provided you have the rights, of course), you can easily upload them to your Flickr account via your right-click menu in Firefox.

ErrorZilla Plus

ErrorZilla Plus is a modification to the previously mentioned ErrorZilla Firefox extension, which adds useful options to the "Server not found" page when you follow a a dead or problematic link. The difference: ErrorZilla Plus adds a Proxify option that re-tries the unreachable URL using a web proxy—perfect for getting around your offices IT lockdown blocks or, as the extension's creator notes, accessing forbidden sites in China.

Got an extension you've seen brewing in the Firefox add-ons experimental labs that you think's worth a mention? Let's hear about it in the comments. Oh, and if you don't feel like registering to try these experimental extensions out yourself, there's always BugMeNot.